The present invention relates to clean rooms and more particularly to air diffusers and filter units supportable on a ceiling gridwork over a clean work area.
In the manufacture of electronic components, the production of certain pharmaceutical agents or compounds and in the performance of certain medical surgery, it is necessary or desirable to control the temperature, humidity and dust conditions of the air within the room or in the work area. In one example of clean room construction, the ceiling of the particular room or work area is formed with a plurality of side-by-side air filtration or diffuser units. Each of the units includes a hood or air plenum and a high efficiency filter. The unit is supported upon an inverted T-bar type ceiling gridwork. The filters employed in such units are HEPA filters. These filters ordinarily have particle efficiencies exceeding 99.97% for 0.3 micron diameter particles as determined by the Army Chemical Corp. D.O.P. Test.
The diffuser units are usually prefabricated at a manufacturing facility prior to actual installation at the job site. Once installed on the ceiling support gridwork, the diffusers are connected to elongated supply ducts which supply compressed air to the units. An example of one such clean room facility may be found in U.S. Pat. No. 3,323,437, entitled FILTER SYSTEM, and issued to J. V. Knab on June 6, 1967. The diffuser or plenum unit disclosed in the aforementioned U.S. Patent includes a filter receptacle within which is supported the filter medium. The filter is preferably permanently sealed into the filter receptacle by means of a suitable sealant such as silicon construction cement.
In certain applications, it has been found undesirable to employ a diffuser unit including a permanently installed filter element. Such diffuser units are essentially "throw away" units and when replaced require disassembly of the ceiling. During such disassembly, contaminants may be introduced into the area above the ceiling. Also, such replacement may be difficult, time-consuming and fairly expensive.
Therefore, it is highly desirable to employ a diffuser unit having a replaceable filter panel or filter element. Examples of various replaceable filter mounting arrangements may be found in U.S. Pat. No. 3,247,652, entitled MEANS FOR MOUNTING FILTER UNITS IN AIR DUCTS, issued on Apr. 26, 1966 to H. C. Annas et al; U.S. Pat. No. 3,740,934, entitled AIR FILTERING UNIT INCLUDING A CLAMPING ASSEMBLY, issued on June 26, 1973 to B. R. Shuler; U.S. Pat. No. 3,780,503, entitled LOW PROFILE FILTER SYSTEM, issued on Dec. 25, 1973 to I. M. Smith; U.S. Pat. No. 3,788,046, entitled APPARATUS FOR FILTERING GASES HAVING A MOVABLE FILTER BAG UNIT, issued on Jan. 29, 1974 to Kaeppler et al; and U.S. Pat. No. 3,870,490, entitled FILTER AND SEAL, issued on Mar. 11, 1975 to Jerome J. Landy.
In certain applications, however, especially those relating to pharmaceutical production, the area around the HEPA filter within the filter housing may become contaminated with the product being manufactured due to the aspirating effect of the air leaving the filter. To prevent such an effect, a complete seal must be provided around the filter panel. Such a seal is not accomplished by heretofore available units in a sample, easily employed manner. Also, unless the filter housing is effectively sealed, contamination may be introduced into the clean room environment from above the ceiling.
In pharmaceutical production, the diffuser units may be positioned over only one production area in the plant. Problems are then experienced with keeping the ordinary plant air out of the clean air area. Commonly, the work area is isolated with plastic curtains. Typically, these are attached to the ceiling and run completely around the filter diffusers dropping within a few inches of the floor. Typical installations only provide a curtain/ceiling fit or seal which permits contaminated or dirty air in the surrounding area to be aspirated into the clean air area at the ceiling.
Further, it has been found that when hoods or diffuser units are employed only in limited locations, and to screen out contaminants in a conditioning air system in a hospital room, for example, problems may be experienced when there is a high heat load in the controlled space. Due to the basically laminar flow air pattern from the diffuser, these units produce a vertical shaft of cool air extending from the ceiling to the floor. When the conditioned and filtered air is considerably cooler than the room air, the air shaft has an even stronger tendency to move directly to the floor. One manner of preventing this phenomenon is to provide a larger supply air volume at a lower temperature difference and increase the number of diffuser units employed above that are necessary for cleanliness alone. This, of course, is a fairly expensive way to solve the problem.